Introduction

We saw in paragraph B.2 that interfering wave vectors influence the signal and in particular the cosine term . In the case of two waves that are perfectly monochromatic and of the same wave length, the interference signal is written as:

This paragraph aims to study the influence of the spatial width of the source, where the waves are issued from, on the contrast of the fringe figures. The influence of the spatial width of the source describes the spatial coherence of light. All interferometric devices seek to generate two waves from a single wave that is produced by a single source. There are many diverse technical solutions to do this, but we can always identify two secondary sources from which the waves that will produce the interferences propagate. In the following section, we will consider the presence of two secondary sources without going into the technical means that are necessary for their creation. The course, Interference: interferometers, will discuss interferometers more in depth. If the reader wishes to know more about this subject, he may consult the aforementioned course.